Hydraulic servo actuator arrangement for an adaptive steering system

ABSTRACT

A servo actuator arrangement for incorporating an adaptive steering system into a conventional power steering mechanism, utilizing a fluidic signal controlled three-way open-center servo valve and a pressure relief bypass in parallel with each other, both in series with the power steering hydraulic supply circuit in order to eliminate the need for a separate actuator fluid pressure source. The servo actuator features a resilient, through-the-port mechanical feedback, and also features a connecting arrangement providing support for the rest of the steering linkage so as to be capable of being inserted into the existing steering gear without additional supports.

United States Patent Kasselmann [54] HYDRAULIC SERVO ACTUATOR Feb. 8,1972 FOREIGN PATENTS OR APPLICATIONS ARRANGEMENT FOR AN ADAPTIVE 426,14l10/1947 Italy ..9l/387 STEERING SYSTEM 79,979 1950 Czechoslovaki ..9H469 [72] Inventor: John T. Kasselmann, Southfield, Mich. v PrimaryExaminer paul E. Maslousky [73] Assignee: The Bendix CorporationAttorney-John R. Benefiel and Flame, Hartz, Smith and 22 Filed: Mar. 20,1970 [21] Appl. No.: 21,323 ABSTRACT A servo actuator arrangement forincorporating an adaptive [52] US. Cl ..91/387, 91/417, 91/469 smeringsystem into a conventional POwer steering 51 ..FlSb 13/16, Fl 5b 15/17mechanism, utilizing fluidic signal three-Way [58] Field of Search..91/387, 47, 469, 417 Wen-center SW0 valve and a P relief bypass inParallel with each other, both in series with the power steering hydrau-[56] References Cited lic supply circuit in order to eliminate the needfor a separate actuator fluid pressure source. The servo actuatorfeatures a UNITED STATES PATENTS resilient, through-the-port mechanicalfeedback, and also features a connecting arrangement providing supportfor the rest 2,247,989 7/ I941 C1ta ..91/387 of the Steering linkage soas to be capable of being inserted I; i i into the existing steeringgear without additional supports. ensen e 3,316,815 5/1967 Chapin etal... .....91/387 3 Claims, 2 Drawing Figures PATENTEDFEB 8:9723.1640184 SHEET 1 UF 2 JZZH T /2 45162977421 HYDRAULIC SERVO ACTUATORARRANGEMENT FOR AN ADAPTIVE STEERING SYSTEM BACKGROUND OF THE INVENTIONThis invention relates generally to adaptive steering systems, and morespecifically to a hydraulic servo actuator arrangement capable of beingincorporated into a conventional power steering mechanism with a minimumof extra components.

Adaptive steering systems, in which the effect of lateral disturbanceson a vehicle are automatically compensated for by a countering movementof the steering gear impressed thereon by a servo actuator mechanism,have been proposed, representatives of such systems being disclosedincopending US. applications Ser; No. 792,238,'Ser. No. 792,243, and Ser.No. 792,904, all assigned to the assignee of the present application.However, the cost and complexity of such a system must be reduced inorder 'to bring these systems into widespread practical use.

One component in which such simplication would be desirable is the servoactuator used to produce the corrective countering movement of thesteering gear. Elimination of the separate pressure source, simplicationof the complex position feedback arrangement of the prior art systemsand the complicated linkages used to impress the countering compensatingmovements onto the steering system by the servo actuator, all would behighly beneficial in accomplishing this end.

Therefore, it is an object of the present invention to provide such aservo actuator which may be incorporated into existing power steeringsystems without requiring an additional fluid power source and will notinterfere with the normal operation of the power steering unit.

It is another object of the present invention to provide a simplifiedconnection for incorporating the servo actuator into the steeringlinkage without the need for separate supporting structure.

SUMMARY OF THE INVENTION These and other objects which will becomeapparent upon a reading of the specification andclaims are accomplishedby providing a fluidic signal controlled three-way open-center servovalve in parallel with a pressure relief bypass, with both of theseconnected in series in the power steering'supply line. A simplifiedmechanical through-the-port feedback is provided between the actuatorpiston and the servo valve, while a link connection with the steeringmechanism drag link provides support for the steering linkage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof the hydraulic servo actuator installation.

I FIG. 2 is a view of the section 22 in FIG. 1 of the servo'actuatortogether with the associated servo valve and link connection.

DETAILED DESCRIPTION In the following detailed description, certainspecificterminology will be used, and a specific embodiment willbedescribed for the sake of clarity, and in order to provide a clearunderstanding of the invention, but the invention is not so limited andmay be practiced in a variety of forms and embodiments.

Referring to the drawings, and specifically to FIG. 1, a con-' Theadaptive steering system 34 includes means for generating fluidiccorrection control signals 36. In the systems disclosed in theapplications referred to above, this is comprised of means forgenerating signals corresponding to the yaw rate of the vehicle ineither direction, vehicle speed, and steering wheel travel in eitherdirection, which signals are appropriately combined and amplified toproduce ap'air ofgfluidic output signals, differences in which willproduce corrective steering movement-in onedirection or the other, in amanner to be disclosed herein. Since the specific means for generatingthese signals does not comprise the present invention, it is not feltnecessary to describe any such system in detail.

These signals are transmitted via hydraulic lines 38 and 40 to the servoactuator assembly 42. This assembly 42 includes a servo valve 44 and aservo motor 46 according to the present I invention.

' with the power steering supply via lines 58, 60 and 62 since flow isnot nonnally interrupted by demands of the servomotor 46. In order toinsure continued flow to the power steering in the event of excessivepressure demands, i.e.,. when the land 50 completely or nearlycompletely blocks the supply port 48, so that insufficient flow for theoperating needs of the power steering unit results, a pressure reliefbypass valve 64 is provided connected via lines 66 and 68 so as to be inparallel with the servo valve 44. Thus if pressure demands of theservoactuator 42 cause the flow path therethrough to be sufficientlyobstructed to cause the pressure drop thereacross to exceed the pressureopening value of the relief valve 66, this valve will open to allowbypass flow to the power steering unit 16, and insure sufficient flow atall times to operate the unit 16.

The servo valve 44 includes a valve spool 68 disposed in the bore 69,having lands 70, 72 as well as the previously mentioned lands 50 and 52.This valve spool 68 is stroked by the force created by the differentialcontrol pressure applied to the land ends 70', 72 vialines 38, 40 andcontrol ports 74, 76 to continuously block and open the supply and retumports 50, 52, respectively, or vice versa by movement of the valve spoolin the bore 69.

High pressure leakage past lands 50 and 52 is returned to the pump 32via lines 78, 80-and ports 82, 84 inorder to avoid any effects on thecontrol pressure values exerted on the valve spool ends.

The servomotor 46 includes a piston 86 slidably disposed in a cylinderhousing 88, and having a major diameter 90 and a minor diameter 92.Supply pressure is continuously applied to the annular area of thepiston defined by the difference between the area of the major diameterless the area defined by the minor diameter via annular groove 94communicating with the chamber 96. This biases the piston 86 to the leftas viewed in FIG. 2. Thus, variation of the magnitude of the pressure inchamber 49 can cause the piston to move in either direction or remainstationary.

As described supra, the pressureexisting in the volume 49 betweenlands50 and 52 isapplied to the area of the piston 86 defined by themajor diameter via passage 56 communicating with the chamber 98'. Thispressure will be a function of spool =position, due to the open-centerdesign, as well as all restrictions downstream.

In order to relate pistonposition to'that of the spool, a positionfeedback arrangement is provided comprised of a leaf spring. element.100 engaging the piston 86 at 102 and the valve spool 68'at 104, thespring 100 being pivoted at 106. Movement of the piston 86 to the rightcauses a force to be exerted on the valve spool 68 to return itto-thenull position, i.e., to the point where the pressure force in chamber 98is sufficient to balancethe force created by pressure in chamber 96.Movementto the left causes a reduction in the spring force,

upsetting the force equilibrium on the valve spool 68 and causing thecontrol pressure differential to null the valve spool 68.

The leaf spring 100 utilizes an existing port 56 so that dynamic sealingof the feedback elements is not required.

A centering spring 108 is provided together with an adjusting nut 110 sothat the piston 86 may be centered.

Integral with the housing 88 is a bifurcated portion 112, into whichextends a piston rod 114 integral with the piston 86. This piston rod114 is pinned at 116 or otherwise connected to a drag link end 116 whichextends into the bifurcation and is welded to one end of the drag link22. Extending through a clearance slot 118 in the drag link end 114 is ataper pin 120 carried by the portion 112 onto which is drawn one end ofthe pitman arm 18 by means of the nut 122 and sleeve 124 to create aconnection therebetween. Thus, modal movement by rotation about the-axisof the pin 120 is allowed between the pitman arm 18 and the drag link 22is allowed while modal movement by rotation about the axis of the piston186 and housing 88 is prevented, thus lending support therebetweenagainst this movement.

OPERATION Under normal steering conditions, motions of the pitman arm 18are transmitted to the drag link 22 via pin 120, portion 112, housing88, which acts on the piston 86 due to the hydrostatic lock therebetweento position the transfer motion via rod 114 to the drag link end 116.

In the event the vehicle condition dictates an adaptive correctivesteering motion, the control means 36 creates a pressure difference inlines 38 and which causes a pressure imbalance across the valve spool68, thus causing it to shift either to the right or left depending onthe nature of the correction required. This in turn causes eithergreater or lesser pressure to exist in chamber 98, resulting in a shiftof the piston 86 either to the right or the left until the valve spool68 is nulled by the action of the leaf spring 100.

Movement of the piston 86 causes a shift in the relative position of thehousing 88 and piston 86 which by reacting against the pitman arm 18creates a corresponding axial movement of the drag link 22 via pistonrod 144 to produce the corrective steering action. This relativemovement is accommodated by the clearance slot 118 in the drag link end116.

From this description, it can be seen that lateral, axial, and torsionalsupport is provided for the drag link 22 and connected linkage by thisconnection with the pitman arm 18 while allowing the corrective relativeaxial movement to occur along the line of action of the piston andcylinder.

It should also be appreciated that this actuating element has beenincorporated without the need for a separate fluid supply, and withoutinterfering with the normal operation of the power steering mechanism.In this regard, it should be noted that maximum flow demands of theadaptive steering servo actuator and the power steering unit willnormally occur at different times, i.e., during parking and slow sharpturns, power steering flow demand is at a maximum, whereas the adaptivesteering would not normally be called into play during these operations.Conversely, at high vehicle speeds when the adaptive steering actuatordemand is likely to be at a maximum, the power steering demands arenormally at a minimum. Hence, theexisting constant flow power steeringpumps may be utilized without substantial modification.

It can also be appreciated that an extremely simple servo valve andactuator assembly has been provided which lends itself readily tolow-cost, high-volume production as is appropriate in automotiveapplication.

What is claimed is:

l. A servo actuator comprising:

a source of fluid pressure;

a fluid motor including a chamber defined in part by a movable member;servo valve means including a movable valve member and providing avariable communication between said source of fluid pressure and saidfluid motor in response to movement of said valve member, and alsoincluding a port communicating with said chamber; 7

means causing said movable motor member to move in response to a levelof fluid communication produced by movement of said movable valvemember;

control means for applying a force to move said movable valve member;

feedback means applying a countering force to said valve member inresponse to responsive movement of said motor member to null said servovalve, said feedback means including a feedback member extending throughsaid port and drivingly connected with said movable motor member andsaid movable valve member, whereby position feedback is obtained.

2. The servo actuator of claim 1 wherein said feedback member is apivotally supported leaf spring with one end engaging said movable valvemember and another end engaging said movable motor member.

3. The servo actuator of claim 1 wherein said servo valve is a three-wayopen-center spool valve and wherein said port communicates with saidopencenter.

1. A servo actuator comprising: a source of fluid pressure; a fluidmotor including a chamber defined in part by a movable member; servovalve means including a movable valve member and providing a variablecommunication between said source of fluid pressure and said fluid motorin response to movement of said valve member, and also including a portcommunicating with said chamber; means causing said movable motor memberto move in response to a level of fluid communication produced bymovement of said movable valve member; control means for applying aforce to move said movable valve member; feedback means applying acountering force to said valve member in response to responsive movementof said motor member to null said servo valve, said feedback meansincluding a feedback member extending through said port and drivinglyconnected with said movable motor member and said movable valve member,whereby position feedback is obtained.
 2. The servo actuator of claim 1wherein said feedback member is a pivotally supported leaf spring withone end engaging said movable valve member and another end engaging saidmovable motor member.
 3. The servo actuator of claim 1 wherein saidservo valve is a three-way open-center spool valve and wherein said portcommunicates with said open-center.